Stented vascular graft

ABSTRACT

A vascular graft incorporating a stent into a portion of its length. While various materials may be used for the vascular graft, the graft is preferably an ePTFE graft. The stent is preferably a self-expanding stent, although it may alternatively be a balloon expandable stent. The vascular graft preferably has a continuous inner tubular liner that extends between the opposing ends of the graft and provides a continuous luminal surface for blood contact that is uninterrupted by seams or joints. The length portion of the graft that does not include the stent has a greater wall thickness than does the portion including the stent.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 11/854,735,now U.S. Pat. No. 8,906,081, filed Sep. 13, 2007, which is incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates to the field of vascular graftsincorporating a stent along a portion of the length of the vasculargraft.

BACKGROUND OF THE INVENTION

Vascular grafts incorporating a stent component at a location along thelength of the graft have been described in the patent literature forsome time. Many of these descriptions relate to the use of a stentlocated at at least one end of a vascular graft for the purpose ofsecuring that end of the vascular graft to the luminal surface of thevasculature into which the graft is desired to be implanted. This isdone as an alternative to a sutured anastomosis. Ersek, in 1970, taughta bifurcated vascular graft of Dacron® or Teflon® secured at each of itsthree ends by a stent component; see U.S. Pat. No. 3,657,744.

Other patents teach the use of separate, space-apart stent componentsalong the length of a vascular graft as an alternative way of making astent-graft. Rhodes, in U.S. Pat. No. 5,122,154, and Lee, in U.S. Pat.No. 5,123,917 described expandable vascular grafts incorporatingring-shaped balloon expandable stent components at intervals along thelength of the graft. Various graft materials are described by these twopatents including PTFE (polytetrafluoroethylene), ePTFE (porous expandedpolytetrafluoroethylene), polyurethane and Dacron®. Materials cited forthe stent component include stainless steel and tantalum.

WO84/03036 describes a stent-graft intended for as an arteriovenousgraft for kidney dialysis.

SUMMARY OF THE INVENTION

A stented vascular graft incorporating at least one stent into a portionof its length is described. The at least one stent is preferably locatedat one end of the stented vascular graft. The stent is preferably aself-expanding stent, although it may alternatively be a balloonexpandable stent. Likewise, the stent may be a self-expanding stent thatcan be further balloon expanded. The stent may provide anchoring andresistance to migration of the stented vascular graft followingdeployment and implantation. The stented vascular graft is intended toprovide for simple and quick anastomosis to a body conduit or to aconventional vascular graft, thereby reducing procedural time.

A stent as described herein is a diametrically expandable tubularframework, typically of metal such as stainless steel or nitinol, thatis intended to provide support to a body conduit when implanted byexpansion to cause it to contact the luminal surface of the bodyconduit. It has open spaces between adjacent framework elements of thestent. A conventional vascular graft is defined herein as a tubularconduit capable of conveying blood, without loss of blood through thewall of the vascular graft (unless punctured or otherwise damaged). Astent-graft is a stent provided with a covering of vascular graftmaterial that covers the open spaces between adjacent stent elements.

The stented vascular graft preferably has an inner tubular liner (i.e.,a tubular element) that extends continuously in uninterrupted fashionbetween opposing ends of the graft and is made from polymeric materialstypically used for conventional vascular grafts such as polyester orePTFE; ePTFE is preferred. This continuous inner tubular liner providesa continuous luminal surface for blood contact that is uninterrupted, orsubstantially uninterrupted, by seams or joints. The liner preferablyhas a relatively thin wall. The length portion of the graft that doesnot include the stent preferably has a second, outer layer ofconventional vascular graft material (i.e., a second tubular element)coaxially surrounding the inner layer, thus providing a thicker graftwall thickness in the unstented region. The greater graft wall thicknessin the unstented region provides the desirable attributes of aconventional vascular graft, including good bending properties with kinkresistance, good hoop strength and is readily sutured while providinggood suture strength (resistance to tearing out of sutures).Additionally, for hemodialysis applications, the greater wall thicknessof the unstented region is anticipated to reduce time to achievehemostasis following the withdrawal of a dialysis needle from apenetration through the wall of the stented vascular graft.

Preferably this second graft layer is close to or even juxtaposedagainst one end of the stent component when the stent component islocated at one end of the stented vascular graft. When the stentcomponent is located between the ends of the stented vascular graft,separate length segments of the second graft layer are located close to,or even juxtaposed against each of the ends of the stent component.

If desired, layers of reinforcing materials such as ePTFE film may beapplied to the external surfaces of either or both the inner and outergraft components and/or over the stent for desired purposes such as toincrease hoop strength or to aid in joining components.

Although the stented vascular graft may be used for a variety ofarterial and venous applications, it is anticipated to be particularlyuseful as an arteriovenous graft for vascular access during kidneydialysis. A stented end of the graft is preferably intended to providethe distal, venous anastomosis. By eliminating the conventional sewnanastomosis at the distal end of such dialysis grafts, it is anticipatedthat the rate of graft failure due to intimal hyperplasia at the outflowanastomosis (a common failure mode of these grafts) will besignificantly reduced. Accordingly, the stented end of the stentedvascular graft may be referred to herein as the distal end while theopposing, unstented end may be referred to as the proximal end. It isrecognized that in some implant applications that this relationship maybe reversed.

While it is preferred that the stented vascular graft is provided with astent located at one end, it is apparent that both ends may be providedwith stents. Likewise, one or more stents may be provided at locationsbetween the ends of the graft. The stented vascular graft can be made ina variety of forms including various lengths and inside diameters. Itmay also be tapered along the length of the device so that the insidediameter is different at the opposing ends. Incorporation of taperedsections along the length of the device may be particularly desirablefor some dialysis graft applications. Dialysis grafts are often providedwith a smaller inside diameter at the arterial end than at the venousend. A tapered length section may be located closer to either end of thegraft, or the taper may exist as a uniform, gradual taper extendingbetween the graft ends.

The unstented portion may also be provided with reinforcing rings orspirals attached to the exterior surface; these exterior reinforcingcomponents may be made so as to be removable by a practitioner.Commercial vascular grafts of this type are available from W. L. Gore &Assoc., Flagstaff Ariz. 86003; see, for example, product no.SRRT06060080L. The unstented portion may also be provided with interiorreinforcing in a manner taught by U.S. Pat. No. 5,747,128 to Campbell etal.

Likewise, particularly for hemodialysis applications, the unstentedportion may be provided with a layer of a self-sealing elastomer betweeninner and outer ePTFE layers in a fashion similar to the vascular grafttaught by Schanzer in U.S. Pat. No. 4,619,641. The unstented portion mayalso be provided with other means of rendering the porous graft materialnon-porous or less porous if desired, such as by the use of coatings ornon-porous or reduced porosity films applied to any portion or surfaceof either the inner or outer graft component. Coatings may also beapplied to fill or substantially fill microscopic void spaces betweenthe opposing graft surfaces.

The device may also be made to be bifurcated or trifurcated, with anycombination of the device ends provided with a stent or not. Thesemultiple-ended devices may have particular utility in applications whereit is desirable to re-perfuse vessels that have been cut off from theirnatural blood supply by another procedure. The larger end of the devicemay be connected to a blood source such as the aorta and the smallerends may be used to re-perfuse smaller vessels (e.g., renal arteries).Still other applications would allow the device to be used to extend thelength of a previously placed conventional vascular graft by insertingthe stent end into an end of the previously placed graft.

As with other vascular grafts, the stented vascular graft may beprovided with known therapeutic agents (e.g., any of variouspharmaceutic agents; anticoagulants such as heparin, etc.). WO02/26281A1provides a representative list of such agents, although the list is notintended to be limiting as to agents that might be used. These agentsmay be applied to the abluminal and/or luminal surfaces, and/or may beincorporated into the void space of the porous microstructure of thevascular graft tubing (e.g., ePTFE tubing). The application of theagents may be by any known means (e.g., such as coating) that aresuitable for attachment of the desired agent to the stented vasculargraft

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the stented vascular graft.

FIG. 2 is a longitudinal cross section of a basic embodiment of thedescribed vascular graft.

FIG. 3 is a longitudinal cross section of an alternative embodiment ofthe described vascular graft that adds a layer of externalreinforcement.

FIG. 4 is a longitudinal cross section of the described vascular graftof FIG. 3 with additional layers of film and further having a flared endat the end of the stent.

FIG. 5 is a longitudinal cross section of the described vascular graftshowing a self expanding stent constrained in a diametrically compactedstate as it may be introduced into the vasculature.

FIG. 6 is a longitudinal cross section showing the vascular graft havingthe compacted stent as shown in FIG. 5 inserted into and deployed in thevasculature.

FIG. 6A is an alternative embodiment to that shown in FIG. 6.

FIGS. 7 and 8 are perspective views showing respectively bifurcated andtrifurcated versions of the vascular graft with the stents deployed intothe vasculature.

FIGS. 9A and 9B show embodiments useful for cardiac applications.

FIGS. 10A-10E show various aspects of a preferred constraining sheathand delivery system.

FIGS. 11A-11E show various aspects of the manufacture of theconstraining sheath and compacting and loading of the stent portion intothe constraining sheath.

FIG. 12 is a longitudinal cross section of an alternative constrainingsheath and delivery system.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 describes a perspective view of the stented vascular graft 10wherein, in the embodiment shown, a stent 12 is affixed to one end of atubular vascular graft 14. The graft 14 in the region of the stent 12has a wall thickness 16 that is less than the wall thickness of thegraft 14 in the unstented region. The wall thickness 17 in the unstentedregion is at least about 10% thicker than the thickness 16 of thestented region. The unstented region wall thickness 17 may be 20%, or30%, or 40%, or 50%, or 60%, or 70%, or 80%, or 90%, or 100%, or 150%,or 200%, or 500% or even greater, than the wall thickness 16 of thestented region. It is preferred that the wall thickness 17 of theunstented region be at least about 50% greater than that of the stentedregion.

Wall thickness may be determined by cutting samples of relatively smallsurface area (e.g., 1 mm square) and measuring the thickness of thosesamples with a Mitutoyo model no. 2804-10 snap gauge having a part no.7300 frame. The measurement is made by placing the graft sample betweenthe measuring pads of the gauge and gently easing the pads into contactwith the sample until the pads are in full contact with the sample underthe full force of the spring-driven snap gauge. Preferably, thethickness of each respective region of the stent vascular graft shouldbe the result of averaging three samples from different areas of eachregion. The samples cut from the stented region should be selected fromareas that are not covered by a stent element (e.g., a portion of thestent wire) so that any compression of the graft thickness by the stentelement is not introduced into the thickness measurement.

Wall thickness of the stented and unstented graft ends is preferablydetermined by measurements derived from scanning electronphotomicrographs (SEM's) of longitudinal cross sections of the differentportions of the same stented vascular graft. This is accomplished forePTFE graft materials by first transversely cutting a length sample ofabout at least about 2 cm length from the graft (for a graft wherein thestent and adjacent thicker unstented graft are juxtaposed), whereinabout half of the length of the sample is composed of the stentedportion and the other half of the length of the sample is composed ofthe unstented portion. The quality of the transverse cuts is notimportant as long as the wall thickness between the ends of thetransverse cuts is not affected. It is apparent that for the stentedportion it will be necessary to cut through both the stent material andthe tubular graft material.

The sample is submerged in 100% isopropyl alcohol until fully wet out(color of the ePTFE will change from white to a grey, translucentappearance). The sample is then submerged in liquid nitrogen untilfrozen (at which time the boiling of the liquid nitrogen largely stops).Next, the sample is then cut longitudinally through the wall between thepreviously cut transverse ends on two sides 180 degrees apart (i.e., twocuts on opposing sides made in a direction parallel to the longitudinalaxis of the tubular sample portion) so that the sample is cut in halflongitudinally. The quality of these longitudinal cuts is important asany cutting artifacts that might affect wall thickness must be minimal.Any cutting means that minimizes cutting artifacts is suitable, such assurgical scissors. It will again be necessary to cut through both thestent material and the tubular graft material for the stented sampleportion.

The resulting half-samples are allowed to warm to ambient and thealcohol is allowed to evaporate from each sample portion. Onehalf-sample is chosen for SEM measurement, sputter-coated as necessaryfor SEM photography, and placed onto a sample pedestal with cut edgesfacing up. The sample is placed into the SEM and the cut edges areviewed to look for thickness views with minimal cutting artifacts.Photographic images are made of these appropriate thickness sites withcalibrated measurement bars included with each photo. Wall thickness ofboth the stented portion and the unstented portion is determined fromthe measurement bars or as indicated by the SEM if the particularmachine offers suitable measurement capability.

Stent 12 as shown is a helically wound serpentine wire, secured to theouter surface of tubular vascular graft 14 by a length of tape 19 thatis helically wound over the stent 12. Preferably the tape is of arelatively narrow width that covers only the center portion of the widthof the serpentine winding, leaving the apices exposed. The stentdescribed is only exemplary; it is apparent that a variety of stentdesigns may be utilized effectively with the described stented vasculargraft.

FIG. 2 shows a longitudinal cross section of a basic embodiment of thedescribed stented vascular graft 10. This figure describes how in apreferred embodiment the graft is created by the use of an inner tube22, preferably having a relatively thin wall thickness, that extends forthe entire length of the stented vascular graft (i.e., between bothopposing ends of the stented vascular graft) including through thestented region. This inner tube 22 may provide the luminal surface 23(i.e., typically the blood contact surface) for the stented vasculargraft. Stent 12 is affixed to a portion of the outer surface of thintube 22. A second portion of graft tubing 24 is fitted over theunstented region of inner tube 22. One end of this second portion 24 islocated close to (i.e., adjacent to) the end of stent 12 that isopposite the distal end of the stent vascular graft. By “close to” ismeant within about 2 cm of the end of stent 12. More preferably, thisend of the second portion of graft tubing 24 is within about 1 mm of theend of stent 12. It may also abut (i.e., is juxtaposed against) this endof stent 12.

FIG. 3 is a longitudinal cross section of an alternative embodiment ofthe described stented vascular graft 10 that adds a layer of externalreinforcement 32. For a vascular graft tubing 14 comprised of ePTFE,this reinforcement may be in the form of a helically applied wrap ofePTFE film that provides an increase in hoop strength and in the generalintegrity of the tubular graft 14.

FIG. 4 is a longitudinal cross section of the stented vascular graft ofFIG. 3 with additional layers of film. Additionally, the vascular grafthas a flared end 42 at the common end of the stent 12 and vascular graft14. As shown, the stented vascular graft 10 is optionally provided withan additional layer 44 of film (e.g., ePTFE film) between inner tube 22and the second portion of graft tubing 24 (the outer tubing over theunstented section). This additional, optional intermediate layer 44 offilm may be used for various purposes depending on the filmcharacteristics. For example, it may be used to provide an impermeablebarrier between the inner and outer portions of the stented vasculargraft 10. Likewise, it may be used to vary the permeability of thestented vascular graft 10 through its thickness. Layer 44 may also be amaterial other than film, for example, a layer of elastomer such as asilicone layer to reduce bleeding for hemodialysis graft applicationswhen a dialysis needle is inserted through the graft wall and thenwithdrawn.

FIG. 4 also describes another optional layer of film 46 that is appliedonly in the region of the end of the second portion of graft tubing 24where it terminates against the adjacent end of stent 12. This securingfilm 46 is used to enhance the integrity of the bond between the end oftubing 24 and the underlying inner tube 22. This figure alsoschematically shows the length of stent-securing tape 19 that is thepreferred method of securing stent 12 to the outer surface of inner tube22 or to any additional layers of film (e.g., layers 32 and/or 44) thatare bonded to the outer surface of inner tube 22. An example of the useof stent-securing tape 19 is shown in greater detail in FIG. 1.

FIG. 5 is a longitudinal cross section of the stented vascular graft 10showing a self expanding stent 12 constrained in a diametricallycompacted state as it may be introduced into a body conduit 52 such asthe vasculature (e.g., a vein for an arteriovenous graft). Stent 12 isconstrained in the compacted state by a constraining sheath 54 that ispreferably made of a thin and lubricious material such as ePTFE film. Avariety of deployment mechanisms are known in the art of self-expandingstents; the constraining sheath 54 shown is exemplary only. Sheath 54 ispreferably removable following deployment of stent 12 within the lumenof a body conduit. Constraining sheath 54 is provided with an extendedend 56 which is preferably an extension of the material comprising theconstraining sheath 54. Tension may be applied to end 56 to effectdeployment of the constrained stent, preferably beginning with the endof the stented vascular graft 10 and progressing back toward the end ofthe stent 12 that is juxtaposed against the thicker-walled vasculargraft portion 24 of the device 10. End edges 57 and 58 converge to forma splittable seam for release of the constraining sheath 54 as will befurther described.

FIG. 6 is a longitudinal cross section showing the stented vasculargraft 10 following deployment of the compacted stent 12 describedpreviously in FIG. 5. Deployment resulted from the application oftension to end 56 of constraining sheath 54. The tension was providedmanually by a practitioner while simultaneously holding device 10 in thedesired location with respect to the body conduit 52. Stent 12 is nowself-expanded to provide physical contact with the luminal surface ofbody conduit 52; constraining sheath 54 has been fully removed, also asthe result of the applied tension. FIG. 6A describes an alternative tothat of FIG. 6 wherein the stented portion extends out of the vein,beyond the venotomy created to insert the stent into the vein.

As previously described, the stented vascular graft 10 can be made in avariety of forms including various lengths and inside diameters. It mayalso be tapered along the length of the device 10 so that the insidediameter is different at the opposing ends. One or both ends of device10 may be provided with an attached stent. The device may be bifurcatedor trifurcated, with any combination of the device ends provided with astent or not. FIG. 7 is a perspective view of a bifurcated device 10Bprovided with stents at both of the small diameter ends. The applicationshown depicts a supra-aortic extra-anatomic bypass based off of theascending aorta 74 wherein the large diameter trunk 71 of device 10B isconventionally anastomosed to the ascending aorta. Several of the greatvessel branches 78 are ligated. Stent 12A is located the end of smalldiameter leg 72 of device 10B; this end has been inserted and deployedinto a transected end of the right common carotid artery 75. Stent 12Bis provided at the end of the other small diameter leg 73 of device 10Band has been deployed into a transected end of the subclavian artery 76.The transected end of the left carotid artery 77 is conventionallyanastomosed to small diameter 73 of device 10B. The use of such abifurcated stented vascular graft 10B for a procedure such as depictedby FIG. 7 would be likely to offer a significant reduction in operatingtime.

FIG. 8 is a perspective view of a multi-vessel iliac-based anatomicbypass intended to provide kidney perfusion in the case of an aorticaneurysm 81 that has been repaired with an endoluminal stent-graft thatresults in the renal arteries 82 as well as other arteries (e.g.,hepatic) being starved of blood. The end of the large diameter leg 84 ofdevice 10T is sutured to the right iliac artery 83 in conventionalfashion, while small diameter legs 85 having stented ends are deployedin the renals and other vessels as necessary. The use of such atrifurcated stented vascular graft 10T for the procedure shown isanticipated to offer a significant saving in operating time incomparison to an equivalent surgery using conventional suturedanastomosis.

FIG. 9A is a perspective view of a branched embodiment 10B of thestented vascular graft wherein the large end of the device is providedwith a stent adapted to be connected through the wall of a vessel suchas the ascending aorta 74. It is used in a bypass application to perfusecardiac vessels that were previously blocked. While the small diameterends are shown to be conventionally anastomosed to the cardiac arteries,they may alternatively be stented. It is apparent that bifurcated (asshown), trifurcated or devices having even more branches might be usedfor these cardiac applications. It may be desirable to use a flanged ordouble flanged stent 87 at the large diameter end of the device 10 asshown in the longitudinal cross section of FIG. 9B.

It is apparent from these descriptions that a variety of brancheddevices could be constructed for various applications.

An exemplary stented vascular graft according to the description of FIG.4 was made beginning with a length of ePTFE tubing of 5.8 mm insidediameter and about 0.1 mm wall thickness. This first ePTFE tube had adensity of about 0.4 g/cc and a mean fibril length of about 17 microns.The ePTFE tube was fitted over a 6.0 mm diameter stainless steelmandrel, being certain that the tube was extended to its approximatefull length after fitting onto the mandrel (thereby ensuring that thelength of the tube was not axially compressed). The tube was thenhelically wrapped with four layers of a 1.9 cm wide tape made from ePTFEfilm, wrapping from one end of the tube to the opposite end, so that atany transverse cross section of the film-wrapped tube, four layers filmthickness were typically present on the outer surface of the ePTFE tube.The film used was a small pore size film of about 2.5 microns thicknessmade according to U.S. Pat. No. 5,476,589 to Bacino. The film-wrappedtube and mandrel assembly was then placed into a convection oven set at380° C. for 10 minutes, removed and allowed to cool to ambient.

A second ePTFE tube was obtained, this tube having an inside diameter of6.0 mm and a wall thickness of 0.7 mm. This tube was diametricallydistended by fitting it over a 7.0 mm diameter mandrel, after which itwas removed from the mandrel. Before this second tube had time to beginto recover from the brief diametrical distension, it was immediatelyfitted coaxially over the first, film-wrapped ePTFE tube which remainedon the mandrel over which it was first placed. An approximately 15 cmlength of the first tube was left exposed (i.e., not covered by thesecond ePTFE tube) at one end of the first tube. The fitting of thesecond ePTFE tube over the first was accomplished while ensuring thatthis second tube was also fully extended longitudinally.

The outer surface of this dual-tube composite was then helically wrappedwith four layers of 1.9 cm wide tape made from an ePTFE film, againwrapping from one end of the tubes to the opposite end, with thewrapping extending over the short exposed length of the first tube. Thisfilm had a thickness of about 7.5 microns, an approximate mean fibrillength of about 50 microns (estimated from scanning electronphotomicrographs) and a density of about 0.3 g/cc (for comparison, thedensity of non-porous PTFE is about 2.2 g/cc).

Next, three layers of a 1.3 cm wide tape made from another ePTFE filmwere circumferentially wrapped over the end of the second ePTFE tube atthe end at which a length of the first tube remained exposed (see FIG.4, securing film 46). The film used was a low porosity ePTFE filmprovided with a coating of fluorinated ethylene propylene (FEP) torender it non-porous; the coated film had a thickness of about 2.5microns. These composite films are made as taught by U.S. Pat. No.5,358,516 to Myers et al. The center of the width of this film wasplaced directly over the end edge of the second tube, so that half ofthe film width was located over the outer surface of the end of thesecond tube and the other half of the width was covering the adjacentouter surface of the first tube. The opposite end of the second tube(along with the underlying first tube) was secured to the mandrelsurface with a metallic clip. The dual-tube composite/mandrel assemblywas then placed into a convection oven set at 380° C. for 10 minutes,removed and allowed to cool to ambient.

A stent was provided to be fitted over the exposed length of the firstePTFE tube. While a variety of stent types may be used to create thestented vascular graft, the chosen stent was a helically wound nitinolwire wherein the wire winding included a serpentine patternincorporating apices pointing alternately to opposite ends of the stent.This type of stent is shown in FIG. 1. The wire was of about 0.15 mmdiameter; the amplitude of the serpentine wire pattern (outside wiresurface dimension of one apex to an adjacent, opposing direction apex)was about 2.2 mm. The stent included about 26 helical revolutionsbetween the stent ends, extending for a length of about 4.6 cm betweenthe stent ends when fitted over the exposed length of the first ePTFEtube. The end of the stent adjacent the end of the second tube wasplaced within 1 mm of the end of the second tube, thereby overlyingabout half of the width of film previously circumferentially wrappedaround this location. After aligning the apices of the serpentine wirepattern as shown in FIG. 1, each helical winding of the serpentine wirewas wrapped with a 1.0 mm wide tape generally as shown in FIG. 1 tosecure the stent to the underlying first ePTFE tube. The film used tomake this tape was a low porosity ePTFE film provided with a coating ofFEP to render it non-porous; the coated film had a thickness of about 25microns

Additionally, both ends of the stent were circumferentially wrapped witha wider tape made from the same FEP-coated ePTFE film of widthsufficient to cover about 7 mm of the length of the stent (about threehelical windings of the stent wire). Prior to providing this wrapping atthe end of the stent located at the end of the device, a 6 mm outsidediameter section of hypotube was inserted into the tip of the stent toprovide the flared graft end (per reference no. 42, FIG. 4).

The vascular graft portion of the device (the unstented portion) wasaxially compressed to about 30% of its length to provide it with rapidrecovery generally as taught by U.S. Pat. No. 4,877,661 to House et al.The composite dual tube/stent/mandrel assembly was then placed into aconvection oven set at 320° C. for 10 minutes, then removed from theoven and allowed to cool to ambient. This heating process completed thesecuring of the stent to the underlying ePTFE tubing and was alsorequired as part of the rapid recovery process. After cooling, theassembly was removed from the mandrel.

Finally, following removal of the stented vascular graft assembly fromthe mandrel, the covering ePTFE film located at the end of the stent atthe end of the device, along with any length of the first ePTFE tubeextending beyond the stent end, was transversely trimmed off with ascalpel blade at a distance of from 0.1 mm to 0.4 mm from the end of thestent.

Stented vascular graft 10 may utilize any suitable form of deliverysystem that is capable of maintaining the self-expanding stent in acompacted form prior to deployment and provides necessary means forallowing the stent to deploy under the control of a practitioner.Preferably the delivery system is removable from the body conduit intowhich device 10 has been inserted following stent deployment. Thesedelivery systems can be configured to provide suitable combinations ofstiffness and flexibility when tailored for use with a specific stentdesign to provide for ease of insertion into, for example, a venotomyand to avoid unnecessary bending during the application of tension tothe delivery system to initiate deployment. One possible delivery systemis described by U.S. Pat. No. 6,224,627 to Armstrong et al. FIG. 10A isa longitudinal cross section of stented vascular graft 10 using apreferred delivery system in the form of an everted, corrugatedconstraining sheath 54 that constrains self-expanding stent 12 in acompacted state as necessary prior to deployment. The amplitude of thecorrugations is exaggerated for visual clarity. The corrugations,oriented circumferentially around the tubular portion 94 of sheath 54,provide increased hoop strength to the sheath 54 and offer bettertactile sensitivity to the practitioner during deployment. The use of agreater sheath length resulting from the use of corrugations reduces therequired tensile force necessary to cause removal of sheath 54 anddeployment of endoprosthesis 12 (due to the length of the corrugatedsheath 54 being greater than the length of a similar uncorrugatedsheath).

Sheath 54 has a tubular portion 94 and an end 56 portion that extends toa gripping means 92. The tubular portion 94 of constraining sheath 54 isprovided having an inner layer and outer, everted layer wherein theouter, everted layer of constraining sheath 54 is everted back over theinner layer at the distal end 96 of stented vascular graft 10, with theresult that both ends of the inner and outer, everted layers of thetubular portion 94 of constraining sheath 54 are located where thethicker portion of graft tubing 24 is adjacent the other end 98 of stent12. End 56 of the outer, everted layer of everted, corrugatedconstraining sheath 54 extends away from device 10 to a gripping meansto which it is affixed such as pull ring 92. The tubular portion 94 ofconstraining sheath 54 is provided with a splittable seam as will befurther described. The edges 57 and 58 of end 56 merge with the tubularportion 94 of constraining sheath 54 at the splittable seam. Theapplication of appropriate tension to end 56 results in splitting of thetubular portion 94 of sheath 54 beginning at the location where end 56merges with tubular portion 94. Splitting of the outer, everted layer ofsheath 54 progresses to the distal end 96 of stent 12 and continues withsplitting of the inner layer of sheath 54 which progresses back in theopposite direction. The progression of splitting of the inner layer oftubular portion 94 progressively releases the constraint ofself-expanding stent 12, allowing stent 12 to deploy beginning with end96 and progressing to end 98. This direction is preferred as deploymentin the opposite direction risks pushing the stent out of the incision inthe vasculature through which it was previously inserted.

FIG. 10B is a longitudinal cross section of an alternative form of theeverted, corrugated constraining sheath 54 wherein the inner layer 97 ofthe tubular portion 94 is corrugated while the outer, everted layer 99is not.

FIG. 10C is a perspective view of the device shown in FIG. 10A.Splittable seam 101 is incorporated into the tubular portion 94 ofconstraining sheath 54. Splittable seam 101 may be provided by anysuitable means of weakening the material of sheath 54 such as byproviding a line of perforations made by computer controlled lasercutting. Other means may also be used, including the use of thinmaterials for sheath 54 that have anisotropic strength properties,offering good hoop strength to the sheath but being inherentlysplittable along the length of the sheath.

FIG. 10D shows a perspective view of initiation of deployment of stent12 by the application of tension (shown by arrow 103) to the end 56 ofsheath 54 via ring 92. As described briefly above, this tension 103causes end 56 to become progressively uncorrugated and causes continuingsplitting of sheath 54 along splittable seam 101. The outer, evertedlayer of sheath 54 has been split along splittable seam 101 andwithdrawn, and the inner layer of sheath 54 is shown splitting as italso is withdrawn, allowing release and deployment of constrained stent12. Simultaneously, tension 103 results in withdrawal of sheath 54 frombetween the deploying stent 12 and the adjacent wall of the body conduitinto which it is being deployed.

FIG. 10E describes a longitudinal cross section of the stented end ofdevice 10 according to the embodiment described by FIGS. 10A, 10C and10D. As shown, corrugations 105 may be non-uniform, with thecorrugations 105 of the outer, everted layer 109 of sheath 54 notnecessarily corresponding exactly to (and consequently not preciselymatching) the corrugations 105 of the inner layer 107 of sheath 54.

A preferred tubular material for the partially everted, corrugatedconstraining sheath 54 is made from a laminated film that is a compositeof FEP and ePTFE film wherein the FEP is applied to the ePTFE film as adiscontinuous coating that allows the film to remain porous. Thesecomposite films are made as taught by U.S. Pat. No. 5,358,516 to Myerset al. A preferred ePTFE film for this laminate is taught by U.S. Pat.No. 5,814,405 to Branca.

To make a 5 cm long, partially everted, corrugated sheath, a 65 cmlength of this composite film is paid off onto a slowly rotatingstainless steel mandrel, with the 65 cm length parallel to the length ofthe mandrel. The mandrel is of the diameter desired for the insidediameter of the constraining sheath, the film oriented with theFEP-coated side of the film facing away from the mandrel surface. Thefilm has similar strength properties and tear properties in the lengthand width directions, so the microstructure of the ePTFE may be orientedwith the length of the nodes oriented in a circumferential direction ororiented parallel to the length of the mandrel. Two layers of this filmare applied, after which heat from a source such as a soldering iron,adequate to melt FEP, is applied along a line along the length of theresulting film tube. The direction of rotation of the mandrel isreversed, and two additional layers of the film are applied; thereversal of rotation results in the FEP-coated side of the film facingtoward the mandrel surface. After the fourth layer is complete, the filmis transversely cut with a blade at the end of the mandrel. Finally, atemporary wrap of a tape of helically applied ePTFE film (withoutFEP-coating) is created over the initial four layers to hold them inplace, and the film-covered mandrel is placed into a convection oven setat 320° C. (above the melt temperature of the FEP) for ten minutes.After this time, the mandrel is removed from the oven and allowed tocool to ambient temperature. Following cooling, the temporary overwrapof helically applied ePTFE tape is removed.

A typical resulting film tube has a wall thickness of about 0.020 to0.025 mm.

Next, the resulting film tube is slid toward one end of mandrel untilone end of the film tube extends a short distance (approximately 1 cm)beyond the end of the mandrel. By careful manual manipulation, the endof the tube is everted back over the portion of the tube remaining overthe mandrel surface, until 10-12 cm of the end of the tube is evertedover the adjacent tube portion. This is repeated for the opposite end ofthe film tube, resulting in the tube having two layers in the evertedregion. The tube is then fitted back onto the same mandrel, oroptionally, another mandrel of slightly larger diameter to compensatefor any diameter increase that resulted from the everting process. Thetube and mandrel assembly is then placed into a suitable programmablelaser cutting machine (a suitable machine is, for example, a CO₂ LaserMarker, model ML-G9320F available from Keyence Corporation, WoodcliffLake N.J.). The machine may be previously programmed to cut a line ofperforations for the full length of the film tube; each individualperforation, for example, being about 0.15 mm wide and of about 0.45 mmlength, with adjacent perforations separated by a land of 0.2 mm length.

While still on the mandrel, the sheath is uniformly compressed in anaxial direction to create the corrugations. The sheath is axiallycompressed until its length is 10% of its original, uncompressed length.As shown by FIG. 10E, the everted portion of the tube is corrugatedsimultaneously with the underlying tube portion. This figure also showsthe relative non-uniformity of the corrugations.

FIG. 11A shows a longitudinal cross sectional view of the manufacture ofcorrugated and everted constraining sheath 54. The tubing from which thesheath 54 is to be made has one end everted back over the inner layer ofthe tube, creating an outer, everted layer along the length of thetubular portion 94 of sheath 54. The resulting everted tubular portion94 with inner layer 107 and outer, everted layer 109 (per therelationship described by FIG. 10E) is fitted over a suitable mandrel111, with the mandrel being a snug fit within the everted tubularportion 94. The opposing ends of the tubular portion 94 are thencompressed axially toward each other, causing the corrugations to formalong the length of the sheath 54 as shown in FIG. 11A.

FIG. 11B shows a funnel device 122 useful for compacting aself-expanding stent 12 affixed to one end of stented vascular graft 10and for inserting the compacted stent 12 into a constraining sheath 54.Funnel device 122 comprises a funnel 124 of a type generally known inthe art of manufacturing self-expandable endoprostheses. Othercompaction methods may also be used, for example, iris-type compactiondevices such as described by U.S. Pat. No. 6,629,350. Funnel device 122is split along seam line 122S into two halves 122A, 122B that aresecured together by suitable means such as fasteners 126. Followingcompaction and loading of stent 12 into constraining sheath 54, the twohalves 122A, 122B of funnel device 122 may be disassembled to removestented vascular graft 10. Funnel device 122 has a length of thin-wallmetal tubing 128 removably attached to funnel device 122 at the smallend of funnel 124; the inside diameter of tubing 128 corresponds to theinside diameter of the small end of funnel 124. Tube 128 is aligned toshare a common axial centerline (not shown) with funnel 124. A suitablethin-wall tubing is a stainless steel hypotube made by Microgroup, Inc.,part no. 304H11XX (Meadway Mass.).

Tubular portion 94 of corrugated and everted sheath 54 is next fittedover the outside of tube 128, as shown by FIG. 11C. This is readilyaccomplished by sliding tubular portion 94 directly off of mandrel 111(FIG. 11A) and directly onto the outer surface of tube 128 while one endof mandrel 111 is held abutted against the end of tube 128 that isopposite funnel 124. End 56 of constraining sheath 54 should be locatedadjacent to the end of funnel 124 as shown. FIG. 11D shows stent 12being pulled via temporary traction lines 132 into funnel 124 (nitinolstents may require simultaneous chilling with a refrigerant spray) andon into the lumen of tube 128 as stent 12 is compacted. FIG. 11E showsthe full length of compacted stent 12 contained within the lumen of tube128. Following this step, tube 128 is removed from its attachment tofunnel 124 by moving it away from the funnel while tubular portion 94 ofsheath 54 is held in place around compacted stent 12. With the removalof tube 128, compacted stent 12 is contained within the tubular portion94 of constraining sheath 54. Finally, the two halves 122A, 122B offunnel device are disassembled and separated, allowing removal of thestented vascular graft 10 with the compacted stent 12 contained withinconstraining sheath 54.

Another deployment system somewhat similar to the everted, corrugatedconstraining sheath 54 may be made by using a length of a thin ePTFEtube (e.g., having a wall thickness of about 0.1 mm, density of about0.4 g/cc and a mean fibril length of about 17 microns) and having amicrostructure of fibrils oriented parallel to the length of the tubewherein a portion of the length of the tube has been provided with acoating of a polymer such as a polyimide. Preferably, the coating isimpregnated into the void spaces of the outer surface of the porousmicrostructure of the ePTFE tubing for good adhesion. One means ofachieving this is by the use of a suitable amount of a suitable solventin the coating polymer. The coated ePTFE tube (having a wall thicknessof, for example, about 0.18 mm) has excellent hoop strength but may bereadily split through the wall by tearing in a direction parallel to thelength of the tube. The use of sheath 121 configured as shown allows fordeployment beginning at distal end 96 of stent 12 and progressing toproximal end 127 of stent 12.

FIG. 12 is a longitudinal cross sectional view of this type ofdeployment system. Sheath 121 is fitted around compacted stent 12 bymeans such as previously described, such that the portion of sheath 121surrounding stent 12 everts back over itself at the distal end 96 ofstent 12 and accordingly has an inner layer 123 and an outer layer 125.The proximal end of outer layer 125 continues to extended end 56 that isattached to means such as pull ring 92 intended to enable a practitionerto apply tension to sheath 121 to initiate longitudinal splitting anddeployment of self-expanding stent 12. Preferably, only inner layer 123of sheath 121 is provided with the polymer coating while the underlyingePTFE tube extends to pull ring 92. As previously described, extendedend 56 is split longitudinally to allow it to diverge from the proximalend 127 of stent 12 as well as providing a starting point for splittingof the tubular length of sheath 121. Inner layer 123 and/or outer layer125 may additionally be provided with perforations or slots or othermeans to more easily enable splitting of sheath 121 during deployment.

While particular embodiments of the present invention have beenillustrated and described herein, the present invention should not belimited to such illustrations and descriptions. It should be apparentthat changes and modifications may be incorporated and embodied as partof the present invention within the scope of the following claims.

We claim:
 1. An implantable prosthesis having a length extending betweenopposing ends, comprising: a first polymeric tubular element extendingfor the entire length of the prosthesis, and said first polymerictubular element further including at least two first length portionswherein a first length portion is located at each of the opposing ends,and a second length portion that together with the first length portionsmake up the entire length of the implantable prosthesis; a stentcoaxially located around at least one of the first length portions ofthe first tubular element; a second polymeric tubular element coaxiallylocated around the entire second length portion of the first polymerictubular element wherein the combination of the second polymeric tubularelement and the second length portion of the first polymeric tubularelement does not include a stent; wherein the length of the secondlength portion is greater than a combined length of both first lengthportions, wherein said first tubular element provides an uninterruptedluminal surface extending for the length of the implantableendoprosthesis.
 2. An implantable prosthesis according to claim 1wherein one end of said second tubular element is located adjacent to atleast one end of one of said first stents.
 3. An implantable prosthesisaccording to claim 1 wherein said implantable prosthesis comprisesePTFE.
 4. An implantable prosthesis according to claim 1 wherein atleast one of said first stents is a self-expanding stent.
 5. Animplantable prosthesis according to claim 1 wherein at least one of saidfirst stents is a balloon expandable stent.
 6. An implantable prosthesisaccording to claim 1 wherein said prosthesis is provided with atherapeutic agent.
 7. An implantable prosthesis according to claim 6wherein said therapeutic agent comprises heparin.
 8. An implantableprosthesis according to claim 6 wherein said therapeutic agent isprovided over at least a portion of an inner surface of said prosthesis.9. An implantable prosthesis according to claim 6 wherein saidtherapeutic agent is provided over at least a portion of an outersurface of said prosthesis.
 10. An implantable prosthesis according toclaim 9 wherein a therapeutic agent is provided over at least a portionof an inner surface of said prosthesis.
 11. An implantable prosthesisaccording to claim 10 wherein the therapeutic agent that is providedover at least a portion of an inner surface of said prosthesis isdifferent from the therapeutic agent that is provided over at least aportion of the outer surface.
 12. An implantable prosthesis according toclaim 1 wherein a stent is coaxially located around each of the firstlength portions of the first tubular element.
 13. An implantableprosthesis comprising a tubular element having a length extendingbetween opposing ends of the prosthesis, said length including at leasttwo first length portions and at least one second length portion, eachfirst and second length portions having a wall thickness, and having atleast one stent affixed to at least one of said first length portions ofthe tubular element, wherein said second length portion does not includea stent and wherein the wall thickness of said second length portion isat least about 20% greater than the wall thickness of said first lengthportions exclusive of the wall thickness of the stent, and wherein thelength of the second length portion is greater than a combined length ofthe first length portions.
 14. An implantable prosthesis according toclaim 13 wherein the tubular element extends continuously between theopposing ends of the prosthesis.
 15. An implantable prosthesis accordingto claim 13 wherein the wall thickness of said second length portion isat least about 100% greater than at least one of said first portionswall thickness.
 16. An implantable prosthesis according to claim 13wherein at least one of said stent is a self-expanding stent.
 17. Animplantable prosthesis according to claim 13 wherein said prosthesis isprovided with a therapeutic agent.
 18. An implantable prosthesisaccording to claim 13 wherein at least two first length portionscomprise a said stent.
 19. An implantable prosthesis according to claim13 further comprising a bifurcation.